Ocular Pharmacology
1. Know the clinically relevant ocular pharmacology '''Anti-Infective Eye Preparations''' ANTIBACTERIALS ANTIFUNGALS Fungal infections of the cornea are rare but may occur after agricultural injuries or in hot and humid climates. Orbital mycosis is even rarer, and usually occurs after spread from the paranasal sinuses. Increasing age, debility, or immunosuppression increases likelihood and severity of disease. Most antifungal preparations are not generally available, and are administered under specialist care at the Moorfields Eye Hospital. ANTIVIRALS Herpes simplex infections producing, for example, dendritic corneal ulcers can be treated with acyclovir or ganciclovir. Acyclovir eye ointment is used in combination with systemic treatment for ophthalmic zoster. Slow release ocular implants containing ganciclovir may be inserted to treat immediate sight-threatening retinitis. '''Corticosteroids and other anti-inflammatory preparations''' CORTICOSTEROIDS Corticosteroids administered locally to the eye or given by mouth are effective for treating anterior segment inflammation, including post-operative inflammation. Main dangers of topical corticosteroids are: 'red eye' (infection), 'steroid glaucoma', 'steroid cataract' following prolonged use, thinning of the cornea and sclera. OTHER ANTI INFLAMMATORY PREPARATIONS Antihistamines such as antazoline, azelastine, epinastine are all used to treat allergic conjunctivitis. Sodium cromoglycate, necrodomil sodium and lodoxamide are mast cell membrane stabilisers, and can be used to treat allergic keratoconjunctivitis. NSAIDs such as diclofenac eye drops help prevent inflammation, and may be used pre- and/or post-operatively to minimise swelling. '''Mydriatics and Cycloplegics ''' Antimuscarinics dilate the pupil and paralyse the ciliary muscle. Weak potencies such as tropicamide 0.5% are used to facilitate examination of the fundus of the eye. Cyclopenolate 1% has an action lasting up to 24 hours, and atropine's action lasts up to 7 days. These drugs are used to facilitate refraction in young children. Mydriatics and cycloplegics are used in the treatment of anterior uveitis, usually as an adjunct to corticosteroids. The drug of choice tends to be atropine, which is used to prevent posterior synechiae (adhesion of the ciliary muscles to the lens), and relieve ciliary spasm. Homatropine (action up to three days) or cyclopenolate are used where a shorter duration of action is needed. Phenylephrine is used in diagnostic and therapeutic prodecures, due to its short onset to action time (within 60-90 minutes) and its short acting nature (5-7 hours). '''Treatment of glaucoma''' BETA BLOCKERS Topical application of beta-blocker to the eye reduces intra-ocular pressure effectively in primary open-angle glaucoma, probably by reducing the rate of production of aqueous humour. Oral administration is also effective but rarely used due to side effects. Examples include: betaxolol, carteolol, levobunolol, and timolol. Systemic side effects can occur even with topical application, therefore beta blockers are contra-indicated in patients with bradycardia, heart block, or uncontrolled heart failure. Local side effects include ocular stinging, burning, pain, itching, erythema, dry eyes and allergic reactions including anaphylaxis. PROSTAGLANDIN ANALOGUES AND PROSTAMIDES Prostaglandin analogues increase uveoscleral outflow and thus reduce intra-ocular pressure. They are used to treat ocular hypertension and open-angle glaucoma. Examples include: latanoprost, tafluprost, travoprost and the synthetic prostamide bimatoprost. Side effects include an increase in brown pigment in the eye, especially in those with mixed coloured irides or who are receiving treatment in one eye only. Patient should be monitored before and during treatment. Care is needed in those with brittle or severe asthma, and those with lens defects such as aphakia, pseudophakia, torn posterior lens capsule and anterior chamber lenses. Similarly, care is also needed in those with risk factors for iritis, uveitis, or cystoid macular oedema. SYMPATHOMIMETICS Brimonidine is a selective alpha-2 adrenoceptor antagonist, is thought to lower ocular pressure by reducing production of aqueous humour and increasing uveoscleral outflow. It is licensed for use in patients with intra-ocular hypertension or open-angle glaucoma in whom beta-blockers are inappropriate. It may also be used as an adjunct to first-line drugs in some patients. Apraclonidine is another alpha-2 adrenoceptor antagonist, which is used short-term to delay laser treatment or surgery in patients with glaucoma not adequately controlled by another drug. 1% apraclonidine is used after anterior segment surgery to control intra-ocular pressure. CARBONIC ANHYDRASE INHIBITORS AND SYSTEMIC DRUGS MIOTICS Miotics work by opening the inefficient drainage channels in the trabecular meshwork. Pilocarpine is not generally used for treatement of primary open-angle glaucoma as its side effects such as miosis are poorly tolerated. It is mainly used for primary angle-closure glaucoma and some secondary glaucomas. Darkly pigmented irises may require a higher concentration. Retinal detachment has occurred in susceptible individuals and those with retinal disease, therefore fundus examination is required before beginning therapy with a miotic. Care is also required in those with conjunctival or corneal damage. Intra-ocular pressure and visual fields should be monitored. Mitotics should be used with caution in patients with peptic ulceration, gastro-intestinal spasm, cardiac disease, hypertension, hypotension, marked vasomotor instability, asthma, epilespsy, Parkinson's disease, hyperthyroidism and urinary tract obstruction. Blurry vision may affect performance of skilled tasks such as driving, especially in low light settings. '''Local anaesthetics ''' '''Miscellaneous'''